Geology

In this paper the tectonic behavior of Leukas and Meganisi islands (Ionian Sea) is examined through underwater research carried out in both islands. A possible Late Holocene correlation between coseismic subsidences is attempted and evidenced by submerged tidal notches in both islands. These subsidence events probably occurred after the uplift that affected the northernmost part of Leukas around 4 to 5ka BP. In conclusion, although the whole area was affected by a similar tectonic strain, certain coseismic events were only recorded in one of the two islands and in some cases they affected only part of the study area.

The Sierra Bermeja Pluton (southern Central Iberian Zone, Iberian Massif) is a late-Variscan intrusive constituted by cordierite-bearing peraluminous monzogranites. Detailed field mapping has allowed to disclose the presence of several NE–SW trending longitudinal composite bodies, formed by either aphanitic or phaneritic mesocratic rocks. According to their petrography and geochemistry these rocks are categorised as calc-alkaline lamprophyres and vaugnerite series rocks. Their primary mineralogy is characterised by variable amounts of plagioclase, amphibole, clinopyroxene, biotite, K-feldspar, quartz and apatite. Broadly, they show low SiO2 content (49–56wt.%), and high MgO+FeOt  (10–17wt.%), K2O (3–5wt.%), Ba (963–2095ppm), Sr (401–1149ppm) and Cr (87–330ppm) contents. Field scale observations suggest that vaugneritic rocks and lamprophyres would constitute two independent magma pulses. Vaugneritic dioritoids intruded as syn-plutonic dykes, whereas lamprophyres were emplaced after the almost complete consolidation of the host monzogranites. In this way, vaugnerite series rocks would be an evidence for the contemporaneity of crustal- and mantle-melting processes during a late-Variscan stage, while lamprophyres would represent the ending of this stage.

In this short note, we present the first data on stable isotope composition of the oilfield waters from Carabobo area of the Faja Petrolífera del Orinoco “Hugo Chávez” (Orinoco Oil Belt). From a chemical point of view, the formation waters show a main Na-Cl level (TDS up to 30g/l) with a dilution trend toward Na-HCO3 composition (down to 1g/l). Until now, such a clear net chemical compositional trend was ascribed to a meteoric dilution (fresh/ brackish bicarbonate) of the seawater endmember (the saltiest chloride). The isotope results of this study reveal that the seawater mother water was modified during a high-temperature thrusting event (120–125°C), forming 18O-enriched diagenetic water (up to +4‰), which was diluted in recent times by glacial meltwater and presentday meteoric water. The hypothetical presence of flood by a meteoric paleo-water also offers new hints to explain the low API gravity (<10°API biodegraded, extra heavy oil) and composition of the local crude.

In Gol-e-Gohar metamorphic Complex from south-eastern Sanandaj-Sirjan metamorphic zone (Kerman province, Iran), there are two types of metabasites contain layered metamorphosed lava flows and the younger meta-gabbros. The protoliths formed in the Paleozoic era and were metamorphosed during the early Cimmerian orogenic phase in the late Triassic, under temperatures of 640–680ºC and pressures of ~7–10.5kbar (amphibolite facies). These rocks are garnet-bearing amphibolites, garnet free amphibolites and metamorphosed gabbros. Many mineralogical and chemical aspects of these metabasites are similar, although the layered metabasites show tholeiitic and the meta-gabbros depict alkaline affinities. Evidences such as whole rock geochemical characteristics, Sr and Nd isotopic data, (143Nd/144Ndinitial=0.511913–0.512067; εNd550Ma=-0.31–2.68), relatively flat patterns of chondritenormalized Rare Earth Elements and multi-elemental diagrams, the enrichment in TiO2 (average content ~2.16) and high Zr/Y ratios (3–8), indicate that all of Gol-e-Gohar metabasites are formed in an extentional intracontinental rift zone from tholeiitic to alkaline magmas. The data suggest that the paren magmas could derived by low degrees of partial melting of spinel-lherzolite sources in subcontinental lithospheric mantle. These evidences confirm the existence of extentional environments in southern part of the Sanandaj-Sirjan metamorphic zone in the Paleozoic era, when large extensional depressions developed in the Sanandaj-Sirjan metamorphic zone and underlying asthenosphere ascent and partially melted during this time. Gradually, thick sequences of continental detritic sediments and tholeiitic lava flows accumulated in these troughs. Subsequent magmatic event in the area characterizes by emplacement of alkaline gabbro intrusions. At the early Cimmerian orogeny, these sedimentaryigneous rocks associations metamorphosed and the Gol-e Gohar metabasites formed.

The mid-Cenomanian Mishrif Formation (Fm.) is considered as one of the most important rudist-bearing reservoir horizons in the Sirri Oil Fields of the Persian Gulf. Due to the general heterogeneity of carbonate reservoirs, the use of an integrated approach is helpful for investigating porosity and permeability distribution along with recognizing controlling pore system factors in the reservoir. Thus, for the reservoir characterization of the Mishrif Fm., an integrated approach including facies analysis, diagenetic history and sequence stratigraphic analysis is considered. Detailed petrographic studies showed a total of eight microfacies and seven facies belts, related to inner ramp to the basin of a homoclinal carbonate ramp. Humid climatic condition and tectonic activity, associated with eustatic sea-level fluctuations during the mid-Cretaceous, led to meteoric diagenesis of the Mishrif carbonates during subaerial exposures (mid-Cenomanian and Cenomanian-Turonian disconformities). General diagenetic overprints and modifications include micritization, cementation, dissolution, compaction, dolomitization, pyritization and fracturing. Considering this reservoir in the sequence stratigraphic framework reveals that the reservoir zones development is basically related to the Cenomanian–Turonian sequence boundary, recognized in the three studied wells, and also to the mid-Cenomanian boundary, identified only in one well. In addition, pore system properties were inspected by differentiation of Hydraulic Flow Units (HFUs) within the reservoir. The identified flow units, based on their capability for fluid flow, can be classified into four main rock types with very high-(HFUD), high-(HFUC), medium-(HFUB) and low-quality (HFUA). Accordingly, this study shows that the main part of the Mishrif Reservoir is affected by diagenetic processes related to subaerial exposures, resulting in zones with higher storage capacity and fluid flow rates. So, the study of depositional and diagenetic characteristics of the Mishrif carbonates in the sequence stratigraphy framework is essential to unravel the reservoir heterogeneity, and to describe the reservoir zones and their distribution in the field and regional scale. In addition, observed changes in the thickness of hydrocarbon column are attributed to the different location of the studied wells on the anticline structures, which show a tilted oil-water contact with a slope to the North.

In a recent study of van der Meulen and coauthors, the fossil rodents Fahlbuschia, Pseudofahlbuschia and Renzimys from the Aragonian type area (Calatayud Basin, Spain) were synonimized with Democricetodon. On the basis of the relative chronology provided by Daams and coauthors in an earlier study, these authors construed two evolutionary lineages, distinguished by size. One of these lineages contains Fahlbuschia koenigswaldi (Freudenthal, 1963) and the other one Democricetodon moralesi van der Meulen et al. (2004) but, in view of their great similarity, we consider D. moralesi to be a synonym of F. koenigswaldi.

The relative stratigraphic position of some fossil mammal localities is difficult to establish in the Aragonian type area because it is affected by folds and faults. Early studies of Daams and Freudenthal subdivided the local zone D into D1, D2, D3 and gave a scheme of the stratigraphy in which the fossiliferous locality Valdemoros 1A is considered to be older than Valdemoros 3B. But Daams and coauthors came to the opposite interpretation in a later study, and divided zone D in Da, Db, Dc, Dd. But, new field data presented here enforce the original interpretation in which Valdemoros 1A is older than Valdemoros 3B. This leads to the conclusion that the division of local zone D into Da to Dd has to be discarded, and substituted by the formerly proposed zonation D1-D3.

Chicxulub Crater, formed ~66Ma ago by an asteroid impact on the southern Gulf of Mexico, is the best preserved of the three large multi-ring basins in the terrestrial record. The crater structure is characterized by a semi-circular concentric ring pattern, marking the crater basin, peak ring, terrace zone and basement uplift. Analysis of a grid of 19 seismic reflection profiles using seismic attributes, marker horizons, contour surfaces and 3-D views is used to investigate the stratigraphy of the central zone. We used interactive software and routine applications to map the impact breccias, breccia-carbonate contact and post-impact carbonates. Four horizons marked by high-amplitude reflectors representing high-impedance contrasts were identified and laterally correlated in the seismic images. Complex trace attribute analysis was applied for petrophysical characterization. Surface contour maps of base and top of stratigraphic packages were constructed, which mapped the impactites and post-and pre-impact carbonate stratigraphy. Basin floor, marked by the contact between the impact breccias and overlying carbonates is shown by laterally discontinuous high-amplitude reflectors. Discontinuous scattered reflectors interpreted as the upper breccias beneath the crater floor, have an average thickness of ~300msm. The Paleogene sedimentary units are characterized by multiple reflectors with lateral continuity, which contrast with the seismic response of underlying breccias. The basal Paleocene sediments follow the basin floor relief. Upwards in the section, the carbonate strata are characterized by horizontal reflectors, which are interrupted by a regional unconformity. Onlap/downlap packages over the unconformity record a period of sea level change.

The Pivehzhan iron deposit is located at about 80km southwest of Mashhad, NE Iran. It occur within the Devonian carbonates as lenticular and massive bodies, as well as veinlets of magnetite and iron sulphides, transformed to goethite and haematite by weathering process. The hydrothermal calcite is the most important gangue mineral, which is observed in the form of veins/veinlets and open-space filling. The iron ores are accompanied by some minor elements such as Mn, Ti, Cr, and V and negligible amounts of Co and Ni. The distribution pattern of Rare Earth Elements (REEs) normalized to Post Archean Australian Shale (PAAS), which is characterized by the upward convex, as well as the positive Eu anomalies indicate the activity of reduced and acidic hydrothermal fluids. The negative Ce anomalies of host carbonates, although slight, point to the dominance of anoxic conditions during interaction with hydrothermal fluids. The hydrothermal calcite and quartz coexisting with the iron minerals contain principally fluid, which were homogenized into a liquid phase. The Homogenization Temperature (T H) and the salinity of the analysed fluid inclusions range from 129°C to 270°C and from 0.4wt.% to 9.41wt.% NaCl eq., respectively. The δ 13 C PDB and δ 18 O SMOW values range from-2.15‰ to-5.77‰ (PeeDee Belemnite PDB standard) and from +19.87‰ to +21.64‰ (Standard Mean Ocean Water SMOW standard) in hydrothermal calcite veinlets occurring with iron minerals, and from-0.66‰ to-4.37‰ (PDB) and from +15.55‰ to +20.14‰ (SMOW) within the host carbonates, respectively. The field relations and petrographic examination along with geochemical and isotopic considerations indicate that the Pivehzhan iron deposit was formed through replacement processes by reducing and acid fluids containing light carbon and oxygen isotopes. Variations in the physico-chemical conditions of hydrothermal fluids and their interaction with carbonates were the most effective mechanisms in the formation of this iron deposit. The potential source of iron was probably the basement magmatic rocks from which iron was leached by hydrothermal solutions.

The Konservat-Lagerstätte Menat (Puy-de-Dôme, France) is an outstanding archive of a Paleocene ecosystem, which was deposited in a former maar lake. Excavations during the last century have yielded an extensive flora and fauna record, therefore an overview of the current state of paleontological investigations is given in this paper. Additionally, new results based on excavations from the years 2012 to 2014 are presented. The preservation of organic matter differed strongly between excavation sites, probably influenced by weathering processes. The stratigraphic succession consists mostly of organic-rich clays, intercalated with hard, silicified claystones. In 2013 and 2014 both impression and compression fossils were collected from different outcrops. Compression fossils from organic-rich clays were exceptionally well-preserved and included three-dimensional plant remains. A new database on insect paleobiodiversity was compiled. The occurrence of charcoal in almost all horizons investigated suggests that paleowildfires were frequent during the Paleocene in the vicinity of the paleolake. The results confirm the high potential of the Konservat-Lagerstätte Menat for future paleontological research.

Small perch-like fishes from the Oligocene of the Paratethys have been traditionally assigned to Serranus budensis (Heckel, 1856). A morphological revision of the holotype and specimens previously assigned to S. budensis from the Outer Carpathians, Poland, is provided herein. They are re-assigned to the species Oligoserranoides budensis (Heckel, 1856) — Percoidei incertae sedis. New specimens assigned to Ol. budensis from the Outer Carpathians, Poland, are introduced. Our results reveal that Ol. budensis is very similar to the species Caucasoserranoides morozkiensis, Carpathoserranoides brnoensis, Carpathoserranoides polonicus and Oligoserranoides comparabilis, and further studies are necessary to revise the validity of those species. Ol. budensis shares many characters with genera Lutjanus and Ocyurus of the superfamily Lutjanoidea. Ol. budensis differs from Lutjanoidea in having a toothless palatine. The palaeobiogeography of Oligocene small perch-like fishes in the Paratethys is presented and discussed.

In the Tafí del Valle region, in northwestern Argentina, several intrusive bodies of lower Paleozoic age were emplaced in the metasedimentary Puncoviscana Formation, belonging to the Sierras Pampeanas. Four intrusive bodies outcrop in the study area: La Ovejería, El Infiernillo, Loma Pelada and Los Cuartos. La Ovejería and El Infiernillo intrusive bodies represent the I-type magmatism according to their major element contents and show cotectic evolutions similar to those described by Famatinian I-type batholiths. These moderately peraluminous adakitic trondhjemites have characteristic high Sr/Y ratios and low Fe 2 O 3 +MgO+MnO+TiO 2 contents. They are related to high-pressure conditions at the source, where dehydration melting of basaltic rocks may be involved and garnet is retained in the residue leading to generation of HREE depleted melts. The Loma Pelada granites show characteristics of S-type magmatism (low CaO and MgO, and high SiO 2 and K2O contents) typical of granites segregated in the last stages of magmatic differentiation, or anatectic granites. They show an increasing peraluminosity due to garnet entrainment and they are related to the anatectic melts generated in the Puncoviscana Formation. Both the Loma Pelada and Los Cuartos granitoids include samples with intermediate geochemical characteristics that range between those of the El Infiernillo and La Ovejería and the regional metasedimentary rocks. These characteristics could be explained by assimilation processes involving the I-type intrusive magmas and the metasedimentary host rocks or by hybridization processes between trondhjemitic I-type magmas as La Ovejería and El Infiernillo and anatectic S-type melts.

The earliest Svecofennian magmatism in southern Finland has been dated at 1.90-1.88Ga. As an example of this, the Orijärvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. Here, we report geochemical and Sm-Nd isotope data from intrusive and extrusive samples, combined with zircon U-Pb and Lu-Hf isotopes for granodiorites from both study areas. The samples range from gabbros to granites and indicate a subduction-related continental margin setting. The zircons from the Orijärvi granodiorite define an age of 1892±4Ma whereas the Enklinge granodiorite yields an age of 1882±6Ma. Several inherited ages of 2.25-1.95Ga as well as younger ages of 1.86-1.80Ga were found in the Enklinge granodiorite. The initial εNd values from the mafic rocks from both locations fall in the range +1.1 to +2.9 whereas the felsic rocks exhibit initial εNd values of -0.4 to +1.2. The magmatic zircons from the Orijärvi and Enklinge granodiorites show average initial εHf values of -1.1 (at 1892Ma) and zero (at 1882Ma), respectively, each with a spread of about 7 ε-units. The initial εHf values for the inherited zircons from Enklinge range from +3.5 to +7.6 with increasing age. The Sm-Nd data indicate that the mafic rocks were derived from a “mildly depleted” mantle source while the felsic rocks show larger crustal contribution. Also, the variation in εHf values indicates minor mixing between mildly depleted mantle derived magmas and crustal sources. U-Pb ages and Hf isotopes for inherited zircons in the Enklinge granodiorite suggest the presence of juvenile Svecofennian “proto-crust” at depth.

The Variscan orogen of NW Iberia contains abundant syn-and post-tectonic granitoids. The post-tectonic granitoids are metaluminous to slightly peraluminous, I-type granites, monzogranites ± granodiorites ± tonalites. The Porriño pluton studied here is a representative example. It consists of two units: i) a pink-red, peraluminous, biotite granite and ii) a gray, metaluminous to peraluminous, biotite (± amphibole ± titanite) monzogranite, including mafic-intermediate enclaves. SHRIMP U-Pb dating yielded 290-295Ma ages for all the units. The mineralogy and geochemistry show that the pink-red granite has features of I-and A-type granites, whereas the gray monzogranite and enclaves are I-types. Sr isotopes show scattered values for the pink-red granite (87 Sr / 86 Sr 295Ma ≈ 0.702-0.710) and uniform values for the gray monzogranite and enclaves (87 Sr/ 86 Sr 295Ma ≈ 0.705-0.706). Geochemical results indicate a peritectic entrainment of clinopyroxene + orthopyroxene ± Ca-plagioclase ± ilmenite ± garnet, and minor accessory phases (± zircon ± titanite ± apatite) into a melt similar to the leucocratic gray monzogranite. A mafic-intermediate source is proposed for the gray monzogranite and its enclaves. Restitic protoliths generated granitic melts with A-type features such as the pink-red granite. The I-type nature of many post-tectonic granitoids could be explained by the previous extraction of S-type syn-tectonic granites that left restites and less fertile rocks. Late orogenic new melting affected the previously unmelted and more mafic lithologies of the lower-middle crust, and gave rise to I-type granitoids. Repeated melting events affecting such lithologies and previous restites could have generated granitic melts with A-type features.